1. Field of the Invention
The present invention relates to a silicone pressure-sensitive adhesive composition and a pressure-sensitive adhesive tape using the same, and particularly to such a composition and pressure-sensitive adhesive tape that exhibit powerful adhesive strength to even silicone rubbers.
2. Description of the Prior Art
Pressure-sensitive adhesive tapes and pressure-sensitive adhesive labels that use a silicone pressure-sensitive adhesive contain a silicone pressure-sensitive adhesive layer that exhibits excellent levels of heat resistance, cold resistance, weather resistance, electrical insulation and chemical resistance, and they are therefore used under severe conditions, such as very high or very low temperatures, where organic resin-based pressure-sensitive adhesives such as acrylic pressure-sensitive adhesives or rubber-based pressure-sensitive adhesives would suffer deformation or degradation.
Moreover, silicone pressure-sensitive adhesives exhibit excellent adhesion to all manner of adherends, including a variety of surfaces that are difficult to bond using acrylic pressure-sensitive adhesives or rubber-based pressure-sensitive adhesives, such as silicone rubbers, silicone release papers, surfaces that have been coated with a release agent, water repellent agent, antifouling agent, paint or coating agent or the like that contains silicone, fluororesins, and surfaces that include a fluororesin component. Accordingly, silicone pressure-sensitive adhesives are ideal for use within pressure-sensitive adhesive tapes used for bonding or fixing a silicone rubber member to another member. However, in recent years there have been growing demands for pressure-sensitive adhesives that are capable of bonding together members of greater mass and capable of producing a bonded interface that is able to withstand greater impact than that achievable using conventional pressure-sensitive adhesives. Namely, there is a need to further improve the adhesive strength of silicone pressure-sensitive adhesives to silicone rubbers.
To provide a specific example, a silicone pressure-sensitive adhesive is used in the pressure-sensitive adhesive tape used for bonding the key tops to a silicone rubber key pad, and in order to ensure superior durability to repeated keystrokes, the pressure-sensitive adhesive tape must be resistant to peeling under all manner of environments from low temperature to high temperature.
When a pressure-sensitive adhesive tape that uses a conventional silicone pressure-sensitive adhesive is employed for the type of application described above, if the shape of the member being bonded is such that a satisfactory bonding surface area cannot be ensured, then detachment of the member may occur as a result of peeling of the pressure-sensitive adhesive tape.
On the other hand, silicone pressure-sensitive adhesive compositions containing an organosilicon compound having B—O—Si bonds are already known (see Patent Document 1), and it has been reported that these compositions provide improved adhesive strength to silicone rubbers, but these compositions have also suffered from inadequate adhesive strength to some silicone rubbers and reduced adhesive strength to adherends other than silicone rubbers.
Furthermore, silicone pressure-sensitive adhesive compositions that use a mixture of a polydiorganosiloxane containing alkenyl groups and a polyorganosiloxane containing no alkenyl groups are also known (see Patent Document 2), and it has been reported that these compositions also provide improved adhesive strength to silicone rubbers, but the adhesive strength of these compositions to silicone rubbers still tends to be inadequate.
Moreover, examples have been reported in which a metal salt of a carboxylic acid is added to a silicone pressure-sensitive adhesive composition to improve the stability of the composition at high temperatures, but there is no mention of a preferred embodiment for achieving superior adhesive strength to silicone rubbers (see Patent Document 3).    [Patent Document 1] JP 07-11228 A    [Patent Document 2] JP 2008-24777 A    [Patent Document 3] EP 0576164 A2